JPWO2019059178A1 - Organic electroluminescent device - Google Patents

Abstract

The present invention provides an organic electroluminescent device having excellent luminous efficiency and brightness. The present invention is an organic electroluminescent element having a structure in which a plurality of layers are laminated between an anode and a cathode formed on a substrate, and the organic electroluminescent element is located between the anode and the cathode. The present invention relates to an organic electroluminescent device having a metal oxide layer, an anode side adjacent to the metal oxide layer, a nitrogen-containing film, and a layer having an average thickness of 0.1 nm or more and less than 3 nm.

Description

The present invention relates to an organic electroluminescent device. More specifically, the present invention relates to an organic electroluminescent element that can be used as a display device such as a display unit of an electronic device or a lighting device.

Organic electroluminescent devices (organic EL devices) are expected as new light emitting devices that can be applied to display devices and lighting.
The organic EL element has a structure in which one or more layers including a light emitting layer formed by containing a luminescent organic compound are sandwiched between an anode and a cathode, and is injected from a hole injected from the anode and a cathode. The energy generated when the electrons are recombined is used to excite a luminescent organic compound to obtain light emission. The organic EL element is a current-driven element, and in order to utilize the flowing current more efficiently, various improvements have been made to the element structure, and various materials for layers constituting the element have also been studied.

In an organic electroluminescent element that excites a luminescent organic compound by using the energy at the time of recombination of holes injected from the anode and electrons injected from the cathode to obtain light emission, holes are injected from the anode and from the cathode. Since it is important that both electron injections are performed smoothly, various materials for the hole injection layer and the electron injection layer have been studied so that hole injection and electron injection can be performed more smoothly. Recently, electron injection that can be applied has been studied. As a layer material, an organic electroluminescent element having a forward structure using polyethyleneimine or a compound modified with polyethyleneimine has been reported (see Non-Patent Documents 1 to 3).

By the way, an organic electroluminescent device in which the layers between the cathode and the anode are all formed of an organic compound is liable to be deteriorated by oxygen or water as a result, and strict sealing is indispensable to prevent their invasion. This causes the manufacturing process of the organic electroluminescent device to become complicated. On the other hand, an organic-inorganic hybrid electroluminescent device (HOILED device) in which a part of the layer between the cathode and the anode is formed of an inorganic oxide has been proposed (see Patent Document 1). In this device, by changing the hole transport layer and the electron transport layer to inorganic oxides, it became possible to use FTO and ITO, which are conductive oxide electrodes, as a cathode, and gold as an anode. This means that there are no restrictions on the electrodes from the viewpoint of element drive. As a result, it is not necessary to use a metal having a small work function such as an alkali metal or an alkali metal compound, and it is possible to emit light without strict sealing. In addition, this HOILED element has a feature that the cathode is usually directly above the substrate and the anode is in the upper electrode. With the development of oxide TFTs, application to large organic EL displays is being studied, and organic EL having a reverse structure has been attracting attention due to the characteristics of n-type oxide TFTs. This HOILED element is expected to develop as a candidate for an inverted organic EL element. Further, such a HOILED device having a layer made of a nitrogen-containing film such as polyethyleneimine having an average thickness of 3 to 150 nm has also been proposed (see Patent Document 2 and Non-Patent Document 4).

Japanese Unexamined Patent Publication No. 2009-70954 Japanese Unexamined Patent Publication No. 2014-168014

Three people outside Tao Xiong "Applied Physics Letters" Vol. 93, 2008, pp123310-1 21 people outside Infa Jou (Yinhua Zhou) "Science" No. 336, 2012, pp327 6 people outside Jianshan Chen "Journal of Materials Chemistry" 2012, Vol. 22, pp5164 5 people outside Yoon Eun Kim (Advanced Hoon Kim) "Advanced Functional Materials" No. 24, 2014, pp3808

As described above, various studies have been conducted on the configurations and materials of organic electroluminescent devices, but further improvement in luminous efficiency and brightness is required for application to display devices and lighting. Development of an excellent organic electroluminescent device is required due to the above characteristics.

The present invention has been made in view of the above situation, and an object of the present invention is to provide an organic electroluminescent device having excellent luminous efficiency and brightness.

As a result of various studies on an organic electroluminescent element having excellent luminous efficiency and brightness, the present inventor has made a nitrogen-containing film on the anode side adjacent to the metal oxide layer between the anode and the cathode, and the average thickness is high. It has been found that the luminous efficiency and brightness of the organic electroluminescent element are improved by forming a thin layer having a thickness of 0.1 nm or more and less than 3 nm, and the present invention has been reached.

The present invention is an organic electroluminescent element having a structure in which a plurality of layers are laminated between an anode and a cathode formed on a substrate, and the organic electroluminescent element is located between the anode and the cathode. An organic electroluminescence characterized by having a metal oxide layer, an anode side adjacent to the metal oxide layer, a nitrogen-containing film, and a layer having an average thickness of 0.1 nm or more and less than 3 nm. It is an element.

The organic electroluminescent device of the present invention is an organic electroluminescent device having an organic-inorganic hybrid type reverse structure that does not require strict sealing, and is excellent in luminous efficiency and brightness. Therefore, it is a display device or a lighting device. Can be suitably used as a material for.

It is the schematic which showed an example of the laminated structure of the organic electroluminescent element shown in this invention. It is a figure which showed the time-dependent change of (a) voltage-luminance characteristic, (b) brightness and voltage under a constant current density (equivalent to 1000 cd / m ² ) of the organic electroluminescent element 1 produced in Example 1. It is a figure which showed the time-dependent change of (a) voltage-luminance characteristic, (b) brightness and voltage under a constant current density (equivalent to 1000 cd / m ² ) of the organic electroluminescent element 2 produced in Example 2. It is a figure which showed the time-dependent change of (a) voltage-luminance characteristic, (b) brightness and voltage under a constant current density (equivalent to 1000 cd / m ² ) of the organic electroluminescent element 3 produced in Example 3. It is a figure which showed the voltage-luminance characteristic of the comparative organic electroluminescent element 1 produced in the comparative example 1. FIG. It is a figure which showed the time-dependent change of (a) voltage-luminance characteristic, (b) brightness and voltage under a constant current density (equivalent to 1000 cd / m ² ) of the organic electroluminescent element 4 produced in Example 4. It is a figure which showed the time-dependent change of (a) voltage-luminance characteristic, (b) brightness under the constant current density (equivalent to 1000 cd / m ² ) of the organic electroluminescent element 5 produced in Example 5. It is a figure which showed the voltage-luminance characteristic of the organic electroluminescent element 6 produced in Example 6. It is a figure which showed the voltage-luminance characteristic of the organic electroluminescent element 7, 8 and comparative organic electroluminescent element 2, 3 produced in Examples 7 and 8 and Comparative Examples 2 and 3. It is a figure which showed the voltage-luminance characteristic of the organic electroluminescent element 9 produced in Example 9. It is a figure which showed the result of having evaluated the variation of the element characteristic by the presence or absence of annealing of the organic electroluminescent elements 2 and 3 produced in Examples 2 and 3. It is a figure which showed the result of having evaluated the variation of the element characteristic by annealing under the atmosphere and the nitrogen atmosphere of the organic electroluminescent elements 1, 2, 10 and 11 produced in Examples 1, 2, 10 and 11.

The present invention will be described in detail below.
It should be noted that a combination of two or more of the individual preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

The organic electric field light emitting element of the present invention is a so-called reverse-structured organic-inorganic hybrid type electric field light emitting element (HOILED element) in which a cathode is formed on a substrate and a metal oxide layer is provided between the anode and the cathode. It is characterized by having a layer composed of a nitrogen-containing film and having an average thickness of 0.1 nm or more and less than 3 nm on the anode side adjacent to the metal oxide layer. The point of the organic electric field light emitting element of the present invention is to reduce the electron injection barrier due to the dipole between the metal of the metal oxide and the nitrogen in the nitrogen-containing film and the dipole in the nitrogen-containing film. The substance and the nitrogen-containing film material are arranged (for example, laminated) in a desired direction (in the order of the metal oxide and the nitrogen-containing film material with respect to the direction of electron injection). It can be said that a thin layer having an average thickness of 0.1 nm or more and less than 3 nm of the present invention is suitable for the latter dipole. The reason is that in the case of ultra-thin films, the orientation of the molecules generated at the interface can be almost inherited in the nitrogen-containing film, but in the case of thick films, it is expected that the dipoles will be oriented in the opposite direction due to the three-dimensional structure of the molecules. This is because the dipoles may be offset. Because of this principle, the element structure (configuration) can be freely selected.
As long as the organic electroluminescent device of the present invention has the above characteristics, the number of other layers, the materials constituting the other layers, and the order of lamination are not particularly limited, but the metal oxide layer and the nitrogen-containing compound layer are not particularly limited. Is preferably between the cathode and the light emitting layer. The nitrogen-containing compound has excellent electron injection characteristics, and an organic electroluminescent device having such a layer structure has high electron injection characteristics, and is an element having excellent luminous efficiency.

The nitrogen-containing film used in the organic electroluminescent element of the present invention includes (1) a nitrogen-containing film formed of a nitrogen-containing compound on a metal oxide layer, and (2) formed of a nitrogen-containing compound on a metal oxide layer. High nitrogen-containing film formed, (3) Nitrogen-containing film formed by decomposing a nitrogen-containing compound on a metal oxide layer, (4) Formed by decomposing a nitrogen-containing compound on a metal oxide layer There are a total of four types of high nitrogen-containing films.
The reason why the performance of the organic electroluminescent device is improved by forming such a film is presumed as follows.
First of all, when it contains a nitrogen atom, its lone pair of electrons tends to form a bond with the metal atom in the substrate. The polarization between the metal-nitrogen bond will exhibit strong electron injection properties. It is satisfied in all the nitrogen-containing films (1) to (4) above. More preferably, the above (2) having a high ratio of nitrogen atoms having a lone electron pair is suitable.
In the above (3) and (4), it is expected that the film will have nitrogen atoms present at high density due to the decomposition phenomenon related to film formation, and as a result, various metal-nitrogen bonds will appear. It is expected. And it is considered that there is also a stronger metal-nitrogen bond than before. Further, depending on the state of decomposition, the nitrogen atom fraction may be relatively increased due to the disappearance of other components such as unnecessary carbon, and as a result, a more suitable environment may be realized (4). .. In these nitrogen-containing membranes, since the origin of the main nitrogen is a metal-nitrogen bond, it is expected that nitrogen atoms are accumulated at a higher density than the physical adsorption of ordinary molecules. Due to these factors, it is considered that having such a nitrogen-containing film makes the organic electroluminescent device excellent in luminous efficiency, device drive stability, and device life. In fact, the phenomenon caused by the decomposition of the nitrogen-containing compound can be proved by X-ray photoelectron spectroscopy, which is one of the surface analysis methods. Specific results will be shown in Examples, but by using a compound containing nitrogen and carbon as constituent elements as the nitrogen-containing compound and performing a treatment to decompose this compound, the carbon: nitrogen ratio (CN ratio) is 2: It has been observed that the nitrogen ratio is high from 1 to 1: 1. At the same time, an increase in the half width of the nitrogen spectrum was observed by the above treatment, which indicates the expansion of the chemical environment and suggests the appearance of a stronger metal-nitrogen bond.
Therefore, it is considered that the fact that the base of the layer made of the nitrogen-containing film is a film containing a metal element also greatly contributes to the development of the effects of the organic electroluminescent device of the present invention as described above.

The nitrogen-containing films (1) and (2) above are films made of nitrogen-containing compounds formed adjacent to the metal oxide layer, that is, the nitrogen-containing compounds are formed without decomposition. The nitrogen-containing film (2) is formed by using a nitrogen-containing compound having a high ratio of the number of nitrogen atoms to the total number of atoms constituting the nitrogen-containing compound.
The method for forming the nitrogen-containing film of (1) and (2) above is not particularly limited, but a method of applying a solution of the nitrogen-containing compound so as to be adjacent to the metal oxide layer and then volatilizing the solvent is preferably used. ..

The nitrogen-containing films (3) and (4) above are films formed by decomposing a nitrogen-containing compound on a metal oxide layer, but some of the nitrogen-containing compounds are not decomposed. May be good. Preferably, all of the nitrogen-containing compounds are decomposed.
The method for forming the nitrogen-containing film of (3) and (4) above is not particularly limited, but a method of applying a solution of the nitrogen-containing compound to the metal oxide layer and then decomposing the nitrogen-containing compound to form the film is preferably used. Be done.

The point that the average thickness of the layer made of the nitrogen-containing film is 0.1 nm or more and less than 3 nm is a major feature of the organic electroluminescent device of the present invention.
Non-Patent Document 4 discloses that the work function is lowered and the barrier of electron injection is lowered by using polyethyleneimine as a material for forming an electron injection layer of a HOILED element having an inverted structure. In Non-Patent Document 4, the change in the work function due to polyethyleneimine increases as the thickness of the polyethyleneimine layer becomes thinner, but the effect is the same between the case where the thickness of the polyethyleneimine layer is 8 nm and the case where the thickness is 4 nm. The result suggests that even if the thickness of the layer is made thinner than about 8 nm, no further improvement in the effect can be expected. On the other hand, in the HOILED element having the reverse structure, the present invention contains nitrogen having an average thickness of 0.1 nm or more and less than 3 nm, which is thinner than that disclosed in Non-Patent Document 4 so as to be adjacent to the metal oxide layer. It has been found that by forming a film, an element having excellent luminous efficiency and brightness can be obtained, which is an effect that cannot be predicted from conventional techniques.

The average thickness of the layer made of the nitrogen-containing film may be 0.1 nm or more and less than 3 nm, but is preferably 0.5 nm or more and 2.9 nm or less. It is more preferably 1.0 nm or more and 2.7 nm or less, and further preferably 1.5 nm or more and 2.5 nm or less.
The average thickness of the layer composed of the nitrogen-containing film can be measured by the method described in Examples.

The nitrogen-containing film contains a nitrogen element and a carbon element as elements constituting the film, and the abundance ratio of the nitrogen atom and the carbon atom constituting the film is the number of nitrogen atoms / (number of nitrogen atoms + number of carbon atoms)>. 1/8
It is preferable to satisfy the relationship of.
When the ratio of the number of nitrogen atoms in the nitrogen-containing membrane is high as described above, the total number of metal-nitrogen bonds increases, and as a result, the electron injection characteristics become higher due to stronger polarization. The number of nitrogen atoms / (number of nitrogen atoms + number of carbon atoms) in the nitrogen-containing film is more preferably larger than 1/5.
The abundance ratio of nitrogen element and carbon element in the nitrogen-containing film can be measured by photoelectron spectroscopy (XPS).

Examples of the nitrogen-containing compound include pyrrolidones such as polyvinylpyrrolidone, pyrroles such as polypyrrole or anilins such as polyaniline, and pyridines such as polyvinylpyridine, as well as pyrrolidines, imidazoles, and piperidine. Such as compounds having a nitrogen-containing heterocycle such as pyrimidines and triazines, and amine compounds. Among them, a nitrogen-containing compound having a primary amine structure is preferable. That is, it is one of the preferred embodiments of the present invention that the nitrogen-containing film is a film derived from a nitrogen-containing compound having a primary amine structure.

As the nitrogen-containing compound, a compound having a high nitrogen content is preferable, and polyamines are preferable. Since polyamines have a high ratio of the number of nitrogen atoms to the total number of atoms constituting the compound, they are suitable from the viewpoint of making the organic electroluminescent element have high electron injection property and drive stability.
As the polyamines, those capable of forming a layer by coating are preferable, and they may be low molecular weight compounds or high molecular weight compounds. As the low molecular weight compound, polyalkyleneamines such as diethylenetriamine and pentamethyldiethylenetriamine are preferably used, and as the high molecular weight compound, a polymer having a polyalkyleneimine structure is preferably used. Polyethyleneimine is particularly preferable. Above all, it is one of the preferred embodiments of the present invention that the nitrogen-containing compound is polyethyleneimine or diethylenetriamine.
Here, the low molecular weight compound means a compound that is not a high molecular weight compound (polymer), and does not necessarily mean a compound having a low molecular weight.

Among the above polyamines, using a polymer having a branched structure having a polyalkyleneimine structure in the main clavicle is one of the preferred embodiments of the present invention.
Further, among the above polyamines, it is also one of the preferred embodiments of the present invention to use a polymer having a linear structure having a polyalkyleneimine structure in the main chain skeleton.
Among the polyamines, by using a polymer in which the main chain skeleton has a branched structure or a linear structure, the device drive stability and device life are improved. It is presumed that this is because the polymer having such a polyalkyleneimine structure in the main clavicle is stably present in the device.
The nitrogen-containing film formed adjacent to the metal oxide layer by a polymer having a branched structure or a linear structure having such a polyalkyleneimine structure in the main chain skeleton is the nitrogen-containing film described in (1) above. Become.
The polymer having a linear structure having the polyalkyleneimine structure in the main chain skeleton may be a polymer in which most of the polyalkyleneimine structures forming the main chain skeleton are linearly linked, and a partially branched structure is used. However, 90% or more of the polyalkyleneimine structure forming the main chain skeleton is linearly linked. Preferably, 95% or more are linearly linked, and most preferably 100% of the polyalkyleneimine structure forming the main clavicle is linearly linked.
The branched polymer having a polyalkyleneimine structure in the main clavicle is a branched polyalkyleneimine having a branched structure of 10% or more.

The polyalkyleneimine structure of the polymer having the polyalkyleneimine structure is preferably a structure formed of alkyleneimine having 2 to 4 carbon atoms. More preferably, it is a structure formed of an alkyleneimine having 2 or 3 carbon atoms.

The polymer having a polyalkyleneimine structure may be any polymer having a polyalkyleneimine structure in the main chain skeleton, and may be a copolymer having a structure other than the polyalkyleneimine structure.

When the polymer having a polyalkyleneimine structure has a structure other than the polyalkyleneimine structure, examples of the monomer used as a raw material for the structure other than the polyalkyleneimine structure include ethylene, propylene, butene, acetylene, and acrylic acid. , Styrene, vinylcarbazole and the like, and one or more of these can be used. Further, those having a structure in which a hydrogen atom bonded to a carbon atom of these monomers is replaced with another organic group can also be preferably used. Examples of other organic groups that replace hydrogen atoms include hydrocarbon groups having 1 to 10 carbon atoms that may contain at least one atom selected from the group consisting of oxygen atoms, nitrogen atoms, and sulfur atoms. Can be mentioned.

The polymer having a polyalkyleneimine structure preferably contains 50% by mass or more of the monomers forming the polyalkyleneimine structure out of 100% by mass of the monomer components forming the main chain skeleton of the polymer. .. More preferably, it is 66% by mass or more, and even more preferably 80% by mass or more. Most preferably, the monomer forming the polyalkyleneimine structure is 100% by mass, that is, the polymer having the polyalkyleneimine structure is a homopolymer of the polyalkyleneimine.

The polymer having a polyalkyleneimine structure preferably has a weight average molecular weight of 100,000 or less. By using such a weight average molecular weight and performing heat treatment at a temperature at which the polymer decomposes to form a layer, the organic electroluminescent device can be made more excellent in drive stability. When the polymer having a polyalkyleneimine structure such as polyethyleneimine is the polymer having the above-mentioned branched structure, the weight average molecular weight of the polymer is more preferably 10,000 or less, still more preferably 100 to 100. It is 1000.
When the polymer having a polyalkyleneimine structure is the polymer having the linear structure described above, the weight average molecular weight of the polymer is more preferably 250,000 or less, still more preferably more than 10,000. It is 50,000 or less, particularly preferably more than 10,000 and less than 25,000.
The weight average molecular weight can be determined by GPC (gel permeation chromatography) measurement under the following conditions.
Measuring equipment: Waters Alliance (2695) (trade name, manufactured by Waters)
Molecular weight column: TSKguard colon α, TSKgel α-3000, TSKgel α-4000, TSKgel α-5000 (all manufactured by Tosoh Corporation) are connected in series and used. Eluent: 14304 g of 100 mM boric acid aqueous solution and 96 g of 50 mM sodium hydroxide aqueous solution. Standard substance for solution calibration line in which 3600 g of acetonitrile and 3600 g are mixed: Polyethylene glycol (manufactured by Tosoh)
Measurement method: The object to be measured is dissolved in an eluent so that the solid content is about 0.2% by mass, and the substance filtered through a filter is used as a measurement sample to measure the molecular weight.

Further, when these nitrogen-containing compounds are decomposed on the metal oxide layer, the nitrogen-containing film (3) and the high nitrogen-containing film (4) are obtained. It is considered that the decomposition product of the nitrogen-containing compound can be more densely deposited on the metal oxide layer by using a compound having a high nitrogen content ratio such as polyamines as the nitrogen-containing compound. A nitrogen-containing thin film on such a metal oxide is also one of the inventions of this patent.

The method for forming the nitrogen-containing film is not particularly limited, but a method including a step of depositing the nitrogen-containing compound and a method including a step of applying a solution containing the nitrogen-containing compound on the metal oxide layer are preferable. A method including a step of applying a solution containing a nitrogen-containing compound on the metal oxide layer is more preferable. When the nitrogen-containing film is formed by a method including a step of applying a solution containing a nitrogen-containing compound on the metal oxide layer, the following effects can also be obtained.
The metal oxide layer of the organic electroluminescent device is formed by a method such as a spray pyrolysis method, a sol-gel method, or a sputtering method as described later, and the surface is not smooth and has irregularities. When a light emitting layer is formed on the metal oxide layer by a method such as vacuum deposition, the unevenness of the surface of the metal oxide layer becomes crystal nuclei depending on the type of the component that is the raw material of the light emitting layer, and metal oxidation occurs. Crystallization of the material forming the light emitting layer in contact with the material layer is promoted. Therefore, even if the organic electroluminescent element is completed, a large leak current may flow and the light emitting surface may become non-uniform, making it impossible to obtain an element that can withstand practical use.
However, when a solution is applied to form a layer, a smooth surface layer can be formed. Therefore, when a nitrogen-containing compound layer is formed by coating between a metal oxide layer and a light emitting layer, a light emitting layer is formed. The crystallization of the material is suppressed, so that the organic electroluminescent element having the metal oxide layer can suppress the leakage current and obtain uniform surface emission.

When polyamines are used as the nitrogen-containing compound, water or a lower alcohol can be used as the solvent for the solution containing the nitrogen-containing compound. As the lower alcohol, it is preferable to use an alcohol having 1 to 4 carbon atoms, and methanol, ethanol, propanol, ethoxyethanol, methoxyethanol and the like can be used alone or in combination.

When the nitrogen-containing film is formed by a method including a step of applying a solution containing a nitrogen-containing compound, the concentration of the solution containing the nitrogen-containing compound is not particularly limited, but may be 0.01 to 1% by mass. preferable. It is more preferably 0.05 to 0.5% by mass, and even more preferably 0.1 to 0.3% by mass.

When the nitrogen-containing film is formed by a method including a step of applying a solution containing a nitrogen-containing compound, a spin coating method, a casting method, a micro gravure coating method, a gravure coating method, a bar coating method, a roll coating method, and a wire bar are used. The film can be formed by using various coating methods such as a coating method, a slit coating method, a dip coating method, a spray coating method, a screen printing method, a flexographic printing method, an offset printing method, and an inkjet printing method. Of these, the spin coating method and the slit coating method are preferable because the film thickness can be more easily controlled.

Further, after performing the step of applying the solution containing the nitrogen-containing compound, a step of rinsing with a solvent or a step of washing with ultrasonic waves may be performed.
When rinsing with a solvent, one or more solvents such as water, ethanol, and methoxyethanol can be used.

The step of applying the solution containing the nitrogen-containing compound, the step of rinsing with a solvent, and the step of washing with ultrasonic waves may be performed in an atmosphere or an inert gas atmosphere, but the inert gas atmosphere may be used. It is preferable to do it below. By performing the operation in an inert gas atmosphere, the obtained element becomes an element excellent in brightness and element life.
As the inert gas, helium, nitrogen, argon or the like can be used.

As long as the nitrogen-containing films of (3) and (4) are formed by decomposing the nitrogen-containing compound on the metal oxide layer, the method for decomposing the nitrogen-containing compound is not particularly limited, but nitrogen. It is preferably formed by decomposing the contained compound by heating.
When the nitrogen-containing compound is decomposed by heating, the bond between the metal atom and the nitrogen atom in the metal oxide layer is strengthened, whereby the organic electroluminescent element exhibits high drive stability for a longer period of time. ..
It is one of the preferred embodiments of the present invention that the nitrogen-containing film is formed by decomposing the nitrogen-containing compound by heating.

Therefore, the nitrogen-containing film is most preferably formed by a method of applying a solution containing a nitrogen-containing compound on a metal oxide layer and then decomposing the nitrogen-containing compound by heating. By forming by the method, the effect of suppressing the leak current and obtaining uniform surface emission, and the effect of making the organic electroluminescent element exhibit high drive stability for a longer period of time can be obtained.
Such a method for manufacturing a HOILED element, that is, a method for manufacturing an organic electric field light emitting element having a structure in which a plurality of layers are laminated between an anode and a cathode formed on a substrate, and the above manufacturing method is , A step of applying a solution containing a nitrogen-containing compound on a metal oxide layer, a step of removing a solvent from a coating film of the nitrogen-containing compound, and a heat treatment at a temperature at which the nitrogen-containing compound decomposes. A method for manufacturing an organic electroluminescent element, which includes a step of manufacturing a layer made of a nitrogen-containing film of the present invention, is also one of the present inventions.
In the method for producing an organic electroluminescent device of the present invention, a preferred embodiment of the step of applying a solution containing a nitrogen-containing compound is as described above. Further, a step of rinsing with the above-mentioned solvent or a step of washing with ultrasonic waves may be performed.

The removal of the solvent in the step of removing the solvent from the coating film of the nitrogen-containing compound is preferably performed by heat treatment. A more stable film structure can be obtained by removing the solvent and the like from the film by heat treatment.
The temperature of the heat treatment for removing the solvent is preferably 80 to 180 ° C. More preferably, it is 100 to 150 ° C.

The temperature of the heat treatment (annealing) for decomposing the nitrogen-containing compound or removing the solvent or the like from the film to obtain a more stable film structure is preferably 80 to 200 ° C. The heat treatment time is preferably 1 to 60 minutes, more preferably 5 to 20 minutes.
The temperature and time of the heat treatment may be appropriately set within the above range depending on the type of nitrogen-containing compound. For example, when a polymer having the following polyalkyleneimine structure in the main chain skeleton is used as the nitrogen-containing compound, the decomposition temperature rises as the molecular weight of the polymer increases. Therefore, in consideration of the molecular weight of the polymer, in Examples described later. The temperature and time of the heat treatment can be appropriately set with reference to the heat treatment conditions of.
The heat treatment for decomposing the nitrogen-containing compound may be carried out in an atmosphere or an inert gas atmosphere.
Whether or not the nitrogen-containing compound is decomposed can be confirmed by X-ray photoelectron spectroscopy (XPS) measurement.

The organic electric field light emitting element of the present invention has an anode and a cathode, and one or more organic compound layers sandwiched between the anode and the cathode, and between the cathode and the organic compound layer, It is preferable to have a metal oxide layer and further to have a layer made of the nitrogen-containing film of the present invention between the metal oxide layer and the organic compound layer. Here, the organic compound layer is a layer that includes a light emitting layer and, if necessary, an electron transport layer and a hole transport layer.
Among them, the organic electric field light emitting element of the present invention is an organic-inorganic hybrid type organic electric field light emitting element in which a cathode is formed adjacent to the substrate and a metal oxide layer is provided between the anode and the cathode, and emits light. It has a layer and an anode, an electron injection layer and, if necessary, an electron transport layer between the cathode and the light emitting layer, and a hole transport layer and / or a positive between the anode and the light emitting layer. It is preferable that the element has a hole injection layer. The organic electroluminescent device of the present invention may have another layer between each of these layers, but is preferably an element composed of only each of these layers. That is, it is preferable that the element is such that the cathode, the electron injection layer, and if necessary, the electron transport layer, the light emitting layer, the hole transport layer and / or the hole injection layer, and the anode layers are laminated in this order. In addition, each of these layers may be composed of one layer or may be composed of two or more layers.
As described above, since the nitrogen-containing film has excellent electron injection characteristics, it is preferably used on the electron injection side, that is, on the cathode side. Further, as will be described later, the metal oxide layer is preferably laminated as a part of the cathode or one layer of the electron injection layer and / or a part of the anode or one layer of the hole injection layer.
In the organic electric field element having the above configuration, when the element does not have an electron transport layer, the electron injection layer and the light emitting layer are adjacent to each other. When the device has only one of the hole transport layer and the hole injection layer, the one layer is laminated adjacent to the light emitting layer and the anode, and the device transports holes. When both the layer and the hole injection layer are provided, these layers are laminated in the order of the light emitting layer, the hole transport layer, the hole injection layer, and the anode.

In the organic electroluminescent device of the present invention, as the material for forming the light emitting layer, any compound that can be usually used as the material for the light emitting layer can be used, and even a low molecular weight compound is a high molecular weight compound. Alternatively, these may be mixed and used.
In the present invention, the low molecular weight material means a material that is not a high molecular weight material (polymer), and does not necessarily mean an organic compound having a low molecular weight.

Examples of the polymer material forming the light emitting layer include polyacetylene compounds such as trans-type polyacetylene, cis-type polyacetylene, poly (di-phenylacetylene) (PDPA), and poly (alkyl, phenylacetylene) (PAPA); Poly (para-phenylene) (PPV), poly (2,5-dialkoxy-para-phenylene vinylene) (RO-PPV), cyano-substituted-poly (para-phenylene) (CN-PPV), poly ( Polyparaphenylene vinylenes such as 2-dimethyloctylsilyl-para-phenylene vinylene) (DMOS-PPV), poly (2-methoxy, 5- (2'-ethylhexoxy) -para-phenylene vinylene) (MEH-PPV) Compounds; Polythiophene compounds such as poly (3-alkylthiophene) (PAT), poly (oxypropylene) triol (POPT); poly (9,9-dialkylfluorene) (PDAF), poly (dioctylfluorene-alto-benzo) Thianazol) (F8BT), α, ω-bis [N, N'-di (methylphenyl) aminophenyl] -poly [9,9-bis (2-ethylhexyl) fluorene-2,7-zil] (PF2 / 6am4) ), Poly (9,9-dioctyl-2,7-divinylenefluorenyl) -ortho-co (anthracene-9,10-diyl) and other polyfluorene compounds; poly (para-phenylene) (PPP) , Polyparaphenylene compounds such as poly (1,5-dialkoxy-para-phenylene) (RO-PPP); polycarbazole compounds such as poly (N-vinylcarbazole) (PVK); poly (methylphenyl) Polysilane compounds such as silane) (PMPS), poly (naphthylphenylsilane) (PNPS), poly (biphenylylphenylsilane) (PBPS); further described in Japanese Patent Application No. 2010-230995, Japanese Patent Application No. 2011-6457. Examples thereof include boron compound-based polymer materials.

Examples of the low molecular weight material forming the light emitting layer include a tricoordinated iridium complex having 2,2'-bipyridine-4,4'-dicarboxylic acid as a ligand, and factories (2-phenylpyridine). Iridium (Ir (ppy) ₃ ), 8-hydroxyquinolin aluminum (Alq ₃ ), tris (4-methyl-8 quinolinolate) aluminum (III) (Almq ₃ ), 8-hydroxyquinolin zinc (Znq ₂ ), (1, 10-Phenantroline) -Tris- (4,4,4-trifluoro-1- (2-thienyl) -butane-1,3-geonate) Europium (III) (Eu (TTA) ₃ (phen)), 2, Various metal complexes such as 3,7,8,12,13,17,18-octaethyl-21H, 23H-porphin platinum (II); benzenes such as distyrylbenzene (DSB), diaminodistyrylbenzene (DADSB) Phosphoric compounds; Naphthalene compounds such as naphthalene and Nile Red; Phenantren compounds such as phenanthrene; Crescent compounds such as chrysene and 6-nitrochrycene; Perylene, N, N'-bis (2,5-di-) Perylene compounds such as t-butylphenyl) -3,4,9,10-perylene-di-carboxyimide (BPPC); coronene compounds such as coronen; anthracene compounds such as anthracene and bisstyrylanthracene; Pyrene compounds such as pyrene; pyrane compounds such as 4- (di-cyanomethylene) -2-methyl-6- (para-dimethylaminostyryl) -4H-pyran (DCM); aclysine compounds such as acrydin Compounds; Stilben compounds such as Stilben; thiophene compounds such as 2,5-dibenzoxazolethiophene; benzoxazole compounds such as benzoxazole; benzoimidazole compounds such as benzoimidazole; 2,2'-( Para-phenylenedivinylene) -benzothiazole compounds such as bisbenzothiazole; butadiene compounds such as bistilyl (1,4-diphenyl-1,3-butadiene), tetraphenylbutadiene; naphthalimide such as naphthalimide Compounds; Cumarin compounds such as coumarin; Perinone compounds such as perinone; Oxaziazole compounds such as oxadiazole; Ardazine compounds; 1,2,3,4,5-pentaf Cyclopentadiene compounds such as enyl-1,3-cyclopentadiene (PPCP); quinacridone compounds such as quinacridone and quinacridone red; pyridine compounds such as spirolopyridine and thiadiazolopyridine; 2,2', 7 , 7'-Tetraphenyl-9,9'-Spiro compounds such as spirobifluorene; metallic or non-metallic phthalocyanine compounds such as phthalocyanine (H ₂ Pc), copper phthalocyanine; further, JP-A-2009-155325 Examples thereof include the boron compound materials described in Japanese Patent Application No. 2010-230995 and Japanese Patent Application No. 2011-6458.

The average thickness of the light emitting layer is not particularly limited, but is preferably 10 to 150 nm. It is more preferably 20 to 100 nm, and even more preferably 40 to 100 nm.
The average thickness of the light emitting layer can be measured by a crystal oscillator film thickness meter in the case of a low molecular weight compound and by a contact type step meter in the case of a high molecular weight compound.

When the organic electroluminescent device of the present invention has an electron transport layer, any compound that can be usually used as a material for the electron transport layer can be used as the material thereof, and these may be mixed and used. ..
Examples of compounds that can be used as materials for the electron transport layer include pyridine derivatives such as tris-1,3,5- (3'-(pyridine-3''-yl) phenyl) benzene (TmPyPhB). Kinolin derivatives such as 2- (3- (9-carbazolyl) phenyl) quinoline (mCQ)), pyrimidine derivatives such as 2-phenyl-4,6-bis (3,5-dipyridylphenyl) pyrimidine (BPyPPM), Pyrazine derivatives, phenanthroline derivatives such as basophenanthroline (BPhen), 2,4-bis (4-biphenyl) -6- (4'-(2-pyridinyl) -4-biphenyl)-[1,3,5] triazine Triazine derivatives such as (MPT), triazole derivatives such as 3-phenyl-4- (1'-naphthyl) -5-phenyl-1,2,4-triazole (TAZ), oxazole derivatives, 2- (4- (4- Oxaziazole derivatives such as biphenyl) -5- (4-tert-butylphenyl-1,3,4-oxadiazole) (PBD), 2,2', 2''-(1,3,5-) Imidazole derivatives such as benzyl) -tris (1-phenyl-1-H-benzimidazole) (TPBI), aromatic ring tetracarboxylic acid anhydrides such as naphthalene and perylene, bis [2- (2-hydroxyphenyl) benzothiazolate] Various metal complexes typified by zinc (Zn (BTZ) ₂ ), tris (8-hydroxyquinolinato) aluminum (Alq3), etc., 2,5-bis (6'-(2', 2''-bipyridyl)) Examples thereof include organic silane derivatives typified by syrol derivatives such as -1,1-dimethyl-3,4-diphenylsilol (PyPySPyPy), and one or more of these can be used.
Among these, a metal complex such as Alq ₃ and a pyridine derivative such as TmPyPhB are preferable.

When the organic electroluminescent device of the present invention has a hole transport layer, various p-type polymer materials and various p-type low molecular weight materials are used alone as the hole transport organic material used as the hole transport layer. Alternatively, it can be used in combination.
Examples of the p-type polymer material (organic polymer) include polyarylamine, fluorene-arylamine copolymer, fluorene-bitiophene copolymer, poly (N-vinylcarbazole), polyvinylpyrene, polyvinylanthracene, and polythiophene. Examples thereof include polyalkylthiophene, polyhexylthiophene, poly (p-phenylene vinylene), polytinylene vinylene, pyrene formaldehyde resin, ethylcarbazole formaldehyde resin or a derivative thereof.
These compounds can also be used as a mixture with other compounds. As an example, the mixture containing polythiophene includes poly (3,4-ethylenedioxythiophene / styrenesulfonic acid) (PEDOT / PSS) and the like.

Examples of the p-type low molecular weight material include 1,1-bis (4-di-para-triaminophenyl) cyclohexane and 1,1'-bis (4-di-para-trilaminophenyl)-. Arylcycloalkane compounds such as 4-phenyl-cyclohexane, 4,4', 4''-trimethyltriphenylamine, N, N, N', N'-tetraphenyl-1,1'-biphenyl-4, 4'-diamine, N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1'-biphenyl-4,4'-diamine (TPD1), N, N'-diphenyl-N , N'-bis (4-methoxyphenyl) -1,1'-biphenyl-4,4'-diamine (TPD2), N, N, N', N'-tetrakis (4-methoxyphenyl) -1,1 '-Biphenyl-4,4'-diamine (TPD3), N, N'-di (1-naphthyl) -N, N'-diphenyl-1,1'-biphenyl-4,4'-diamine (α-NPD) ), Arylamine compounds such as TPTE, N, N, N', N'-tetraphenyl-para-phenylenediamine, N, N, N', N'-tetra (para-tolyl) -para-phenylenediamine , N, N, N', N'-tetra (meth-trill) -meth-phenylenediamine (PDA) and other phenylenediamine compounds, carbazole, N-isopropylcarbazole, N-phenylcarbazole and other carbazole compounds. , stilbene, 4-di - para - stilbene compounds such as tolyl aminostilbene, oxazole compounds, such as _{O x} Z, triphenylmethane, triphenylmethane compounds such as m-MTDATA, 1-phenyl-3 -Pyrazoline compounds such as (para-dimethylaminophenyl) pyrazoline, benzine (cyclohexadiene) compounds, triazole compounds such as triazole, imidazole compounds such as imidazole, 1,3,4-oxadiazol, Oxaziazole compounds such as 2,5-di (4-dimethylaminophenyl) -1,3,4-oxadiazole, anthracene, anthracene compounds such as 9- (4-diethylaminostyryl) anthracene, fluorenone , 2,4,7-Trinitro-9-fluorenone, 2,7-bis (2-hydroxy-3- (2-chlorophenylcarbamoyl) -1-naphthylazo) fluorenone compounds such as fluorenone, polyani Aniline compounds such as phosphorus, silane compounds, pyrrol compounds such as 1,4-dithioketo-3,6-diphenyl-pyrrolo- (3,4-c) pyrrolopyrrole, floren compounds such as floren, Porphyrin, metal tetraphenyl Porphyrin-based compounds such as porphyrin, quinacridone-based compounds such as quinacridone, phthalocyanines, copper phthalocyanines, tetra (t-butyl) copper phthalocyanines, metallic or metal-free phthalocyanine compounds such as iron phthalocyanines, copper Metallic or metal-free naphthalocyanine compounds such as naphthalocyanine, vanadyl naphthalocyanine, monochlorogally naphthalocyanine, N, N'-di (naphthalen-1-yl) -N, N'-diphenyl-benzidine, N, N , N', N'-benzidine-based compounds such as tetraphenylbenzidine and the like.

When the organic electroluminescent device of the present invention has an electron transport layer and a hole transport layer, the average thickness of these layers is not particularly limited, but is preferably 10 to 150 nm. It is more preferably 20 to 100 nm, and even more preferably 40 to 100 nm.
The average thickness of the electron transport layer and the hole transport layer can be measured by a crystal transducer film thickness meter in the case of a low molecular weight compound and by a contact type step meter in the case of a high molecular weight compound.

The organic electroluminescent element of the present invention has a metal oxide layer between the cathode and the light emitting layer and / or between the anode and the light emitting layer, but between the cathode and the light emitting layer. It is preferable to have a metal oxide layer both between the light emitting layer and the anode. The metal oxide layer between the cathode and the light emitting layer is used as the first metal oxide layer, and the metal oxide layer between the anode and the light emitting layer is used as the second metal oxide layer. To represent an example of the configuration of the preferred element, the cathode, the first metal oxide layer, the layer composed of the nitrogen-containing film, the light emitting layer, the hole transport layer, the second metal oxide layer, and the anode are adjacent to each other in this order. It is a laminated structure. An electron transport layer may be provided between the layer made of the nitrogen-containing film and the light emitting layer, if necessary. The importance of the metal oxide layer is higher in the first metal oxide layer, and the second metal oxide layer can be replaced with an organic material having an extremely deep minimum unoccupied molecular orbital, for example, HATCN. ..

The first metal oxide layer is a semiconductor or insulator laminated thin film which is a layer composed of one layer of a single metal oxide film, or a layer in which a simple substance or two or more kinds of metal oxides are laminated and / or mixed. It is a layer. Metal elements that make up metal oxides include magnesium, calcium, strontium, barium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, indium, gallium, iron, cobalt, nickel, and copper. , Zirconium, cadmium, aluminum, silicon. Of these, at least one of the metal elements constituting the laminated or mixed metal oxide layer is preferably a layer composed of magnesium, aluminum, calcium, zirconium, hafnium, silicon, titanium, and zinc, and among them, a single metal. The oxide preferably contains a metal oxide selected from the group consisting of magnesium oxide, aluminum oxide, zirconium oxide, hafnium oxide, silicon oxide, titanium oxide and zinc oxide.

Examples of the single layer or a layer in which two or more kinds of metal oxides are laminated and / or mixed are titanium oxide / zinc oxide, titanium oxide / magnesium oxide, titanium oxide / zirconium oxide, titanium oxide / aluminum oxide, titanium oxide / Laminate and / or stack combinations of metal oxides such as hafnium oxide, titanium oxide / silicon oxide, zinc oxide / magnesium oxide, zinc oxide / zirconium oxide, zinc oxide / hafnium oxide, zinc oxide / silicon oxide, calcium oxide / aluminum oxide. Mixed or titanium oxide / zinc oxide / magnesium oxide, titanium oxide / zinc oxide / zirconium oxide, titanium oxide / zinc oxide / aluminum oxide, titanium oxide / zinc oxide / hafnium oxide, titanium oxide / zinc oxide / silicon oxide, Examples thereof include laminated and / or mixed combinations of three types of metal oxides such as indium oxide / gallium oxide / zinc oxide. Among these, a IGZO and electride an oxide semiconductor having good characteristics as a special composition 12CaO · _7Al 2 _{O 3} are also included.
These first metal oxide layers can be said to be electron injection layers and also electrodes (cathodes).
In the present invention, a material having a sheet resistance lower than 100Ω / □ is classified as a conductor, and a material having a sheet resistance higher than 100Ω / □ is classified as a semiconductor or an insulator. Therefore, ITO (tin-doped indium oxide), ATO (antimon-doped indium oxide), IZO (indium-doped zinc oxide), AZO (aluminum-doped zinc oxide), FTO (fluorine-doped indium oxide), etc., which are known as transparent electrodes, are used. The thin film does not fall under the layer constituting the first metal oxide layer of the present invention because it has high conductivity and is not included in the category of semiconductor or insulator.

The metal oxide forming the second metal oxide layer is not particularly limited, but is limited to vanadium oxide (V ₂ O ₅ ), molybdenum oxide (MoO ₃ ), tungsten oxide (WO ₃ ), and ruthenium oxide (RuO ₂ ). ) Etc., or two or more types can be used. Among these, those containing vanadium oxide or molybdenum oxide as a main component are preferable. When the second metal oxide layer is composed mainly of vanadium oxide or molybdenum oxide, the second metal oxide layer injects holes from the anode and transports them to the light emitting layer or the hole transport layer. It becomes more excellent due to its function as a hole injection layer. Further, since vanadium oxide or molybdenum oxide has high hole transporting property itself, it has an advantage that it is possible to preferably prevent a decrease in the injection efficiency of holes from the anode into the light emitting layer or the hole transporting layer. There is. More preferably, it is composed of vanadium oxide and / or molybdenum oxide.

The average thickness of the first metal oxide layer is acceptable from 1 nm to several μm, but is preferably 1 to 1000 nm from the viewpoint of an organic electroluminescent device that can be driven at a low voltage. More preferably, it is 2 to 100 nm.
The average thickness of the second metal oxide layer is not particularly limited, but is preferably 1 to 1000 nm. More preferably, it is 5 to 50 nm.
The average thickness of the first metal oxide layer can be measured by a stylus type step meter and spectroscopic ellipsometry.
The average thickness of the second metal oxide layer can be measured at the time of film formation with a crystal oscillator film thickness meter.

In the organic electroluminescent device of the present invention, known conductive materials can be appropriately used as the anode and the cathode, but it is preferable that at least one of them is transparent for light extraction. Examples of known transparent conductive materials include ITO (tin-doped indium oxide), ATO (antimon-doped indium oxide), IZO (indium-doped zinc oxide), AZO (aluminum-doped zinc oxide), FTO (fluorine-doped indium oxide), and the like. Is raised. Examples of opaque conductive materials include calcium, magnesium, aluminum, tin, indium, copper, silver, gold, platinum and alloys thereof.
Among these, ITO, IZO, and FTO are preferable as the cathode.
Among these, Au, Ag, and Al are preferable as the anode.
As described above, since the metal generally used for the anode can be used for the cathode and the anode, it is possible to easily realize the case where light is taken out from the upper electrode (in the case of the top emission structure), and the above electrode can be used. It can be selected in various ways and used for each electrode. For example, Al is used as the lower electrode, ITO is used as the upper electrode, and the like.

The average thickness of the cathode is not particularly limited, but is preferably 10 to 500 nm. More preferably, it is 100 to 200 nm. The average thickness of the cathode can be measured by a stylus profilometer or spectroscopic ellipsometry.
The average thickness of the anode is not particularly limited, but is preferably 10 to 1000 nm. More preferably, it is 30 to 150 nm. Even when an opaque material is used, it can be used as a top emission type or transparent type anode by setting the average thickness to about 10 to 30 nm, for example.
The average thickness of the anode can be measured at the time of film formation with a crystal oscillator film thickness meter.

In the organic electroluminescent element of the present invention, the method for forming a layer formed of an organic compound is not particularly limited, and various methods can be appropriately used according to the characteristics of the material, but when it can be applied as a solution, it can be applied. Spin coat method, casting method, micro gravure coat method, gravure coat method, bar coat method, roll coat method, wire bar coat method, slit coat method, dip coat method, spray coat method, screen printing method, flexo printing method, offset The film can be formed by using various coating methods such as a printing method and an inkjet printing method. Of these, the spin coating method and the slit coating method are preferable because the film thickness can be more easily controlled. When not coated or when the solvent solubility is low, a vacuum vapor deposition method, an ESDUS (Evaporative Spray Deposition Solution from Ultra-dilution Solution) method and the like can be mentioned as preferable examples.

When the layer formed from the above organic compound is formed by applying an organic compound solution, the solvent used for dissolving the organic compound is, for example, nitrate, sulfuric acid, ammonia, hydrogen peroxide, water, carbon disulfide. , Inorganic solvents such as carbon tetrachloride, ethylene carbonate, ketone solvents such as methyl ethyl ketone (MEK), acetone, diethyl ketone, methyl isobutyl ketone (MIBK), methyl isopropyl ketone (MICK), cyclohexanone, methanol, ethanol, isopropanol, Alcohol-based solvents such as ethylene glycol, diethylene glycol (DEG), and glycerin, diethyl ether, diisopropyl ether, 1,2-dimethoxyethane (DME), 1,4-dioxane, tetrahydrofuran (THF), tetrahydropyran (THP), anisole, Ether-based solvents such as diethylene glycol dimethyl ether (digrim) and diethylene glycol ethyl ether (carbitol), cellosolve-based solvents such as methyl cellosolve, ethyl cellosolve, and phenyl cellosolve, aliphatic hydrocarbon solvents such as hexane, pentane, heptane, and cyclohexane, toluene. , Aromatic hydrocarbon solvents such as xylene, benzene, aromatic heterocyclic solvents such as pyridine, pyrazine, furan, pyrrol, thiophene, methylpyrrolidone, N, N-dimethylformamide (DMF), N, N-dimethyl Amid solvents such as acetoamide (DMA), halogen compound solvents such as chlorobenzene, dichloromethane, chloroform, 1,2-dichloroethane, ester solvents such as ethyl acetate, methyl acetate and ethyl formate, dimethyl sulfoxide (DMSO), sulfolane and the like. Sulfur compound solvent, nitrile solvent such as acetonitrile, propionitrile, acrylonitrile, various organic solvents such as organic acid solvent such as formic acid, acetic acid, trichloroacetic acid, trifluoroacetic acid, or mixed solvent containing these. Can be mentioned.
Among these, a non-polar solvent is preferable as the solvent, and for example, aromatic hydrocarbon solvents such as xylene, toluene, cyclohexylbenzene, dihydrobenzofuran, trimethylbenzene, and tetramethylbenzene, pyridine, pyrazine, furan, and the like. Examples thereof include aromatic heterocyclic solvent such as pyrrole, thiophene and methylpyrrolidone, and aliphatic hydrocarbon solvent such as hexane, pentane, heptane and cyclohexane, and these can be used alone or in combination.

The cathode, anode, and oxide layer are formed by a sputtering method, a vacuum deposition method, a sol-gel method, a spray pyrolysis (SPD) method, an atomic layer deposition (ALD) method, a vapor phase deposition method, a liquid phase film formation method, etc. Can be formed by A metal foil bond can also be used to form the anode and cathode. These methods are preferably selected according to the characteristics of the material of each layer, and the production method may be different for each layer. Among these, the second metal oxide layer is more preferably formed by using a vapor phase film forming method. According to the vapor phase film forming method, the organic compound layer can be formed cleanly and in good contact with the anode without damaging the surface, and as a result, the effect of having the second metal oxide layer as described above is obtained. Becomes more prominent.

For the reason of further improving the characteristics of the organic electroluminescent device of the present invention, for example, a hole blocking layer, an electron blocking layer, or the like may be provided, if necessary. As the material for forming these layers, a material usually used for forming these layers can be used, and the layers can be formed by a method usually used for forming these layers.

The organic electroluminescent device of the present invention does not require strict sealing as compared with an organic electroluminescent device in which all the layers constituting the device are composed of an organic compound, but may be sealed if necessary. .. As the sealing step, a usual method can be appropriately used. For example, a method of adhering a sealing container in an inert gas, a method of forming a sealing film directly on an organic EL element, and the like can be mentioned. In addition to these, a method of encapsulating a water absorbing material may be used in combination.

The organic electroluminescent device of the present invention is an organic electroluminescent device having an inverted structure in which cathodes are formed adjacent to each other on a substrate. The organic electroluminescent device of the present invention may be a top-emission type that extracts light on the side opposite to the side where the substrate is located, or may be a bottom-emission type that extracts light on the side where the substrate is located. ..
Examples of the substrate material include resin materials such as polyethylene terephthalate, polyethylene naphthalate, polypropylene, cycloolefin polymer, polyamide, polyether sulfone, polymethylmethacrylate, polycarbonate and polyarylate, and quartz glass and soda glass. Examples include glass materials, and one or more of these can be used.
In the case of the top emission type, an opaque substrate can also be used. For example, an oxide film (insulating film) is formed on the surface of a substrate made of a ceramic material such as alumina or a metal substrate such as stainless steel. A substrate made of a resin material or the like can also be used.

The average thickness of the substrate is preferably 0.1 to 30 mm. More preferably, it is 0.1 to 10 mm.
The average thickness of the substrate can be measured with a digital multimeter and calipers.

The organic electroluminescent device of the present invention can emit light by applying a voltage (usually 15 volts or less) between the anode and the cathode. Normally, a DC voltage is applied, but an AC component may be included.
The organic electroluminescent element of the present invention can change the emission color by appropriately selecting the material of the organic compound layer, and can also obtain a desired emission color by using a color filter or the like in combination. Therefore, it can be suitably used as a light emitting part of a display device or a lighting device. In particular, a display device combined with an oxide TFT is suitable because of its reverse structure.
Such a display device characterized by including the organic electroluminescent element of the present invention and a lighting device characterized by including the organic electroluminescent element of the present invention are also one of the present inventions.

As described above, the organic electroluminescent device of the present invention has a layer made of a nitrogen-containing film on the metal oxide layer, so that the electron injection characteristics are improved and the luminous efficiency is excellent, and the drive stability of the device and the device are excellent. It also has an excellent life. Such an effect of improving the electron injection characteristics is beneficial not only for organic electroluminescent devices but also for other optoelectronic devices such as solar cells and organic semiconductors, which contributes to performance improvement.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. Unless otherwise specified, "part" means "part by weight" and "%" means "mass%".

The film thickness of the nitrogen-containing film was measured by the following method.
Since the film thickness of the nitrogen-containing film is an extremely thin film, it is difficult to measure it by a measuring method such as a normal contact-type profilometer, and a calculation method using X-ray photoelectron spectroscopy was used. This calculation method was also used and established in "Journal of Physical Chemistry B", Vol. 108, 2004, pp5185, by two people other than Ketul C Popat. Here, the following formula (1) was used to calculate the film thickness of the nitrogen-containing film. (Maruzen Co., Ltd. "X-ray photoelectron spectroscopy")

I _i is the nitrogen 1s orbital strength of the unknown sample, I _i ⁰ is the nitrogen 1s orbital strength of the standard sample consisting of the nitrogen-containing material used for film formation, X _i is the mole fraction, and Z'is the depth from the sample surface. Let λ _{i be} the escape depth of the photoelectron of interest for the element i, λ _{i and i be} the inelastic average free process, and Z ₁ −Z be the film thickness.
The X-ray photoelectric spectroscopic measurement was carried out under the following conditions using a photoelectron spectroscopic measurement device manufactured by Shimadzu Kratos (AXIS-NOVA).
X-ray source: AlKα
Beam output: 100W
PassEnergy: 40eV
Step: 0.1eV

(Manufacturing and characterization of organic electroluminescent devices)
(Example 1)
[1] A commercially available transparent glass substrate 1 with an ITO electrode layer having an average thickness of 0.7 mm was prepared. At this time, the ITO electrode 2 of the substrate used was patterned with a width of 2 mm. After rinsing this substrate with ultrapure water, it was ultrasonically cleaned twice for 5 minutes in a diluted solution of Clean Ace. Then, it was ultrasonically cleaned in ultrapure water for 5 minutes x 2 times, ultrasonically cleaned in acetone and isopropanol for 10 minutes each, and then boiled in isopropanol for 5 minutes. This substrate was taken out of isopropanol, dried by nitrogen blow, and UV ozone washed for 20 minutes.
[2] This substrate was fixed again to the substrate holder of the Miratron sputtering apparatus having a zinc metal target. After reducing the pressure to about 5 × 10 ⁻⁵ Pa, the mixture was sputtered with argon and oxygen introduced to prepare a zinc oxide layer having a film thickness of about 2 nm as the first metal oxide layer 3.
At this time, a metal mask was also used to prevent zinc oxide from being formed on a part of the ITO electrode in order to take out the electrode.
[3] This substrate was ultrasonically cleaned in ultrapure water for 15 minutes, then ultrasonically cleaned in acetone and isopropanol for 5 minutes, and boiled in isopropanol for 5 minutes. This substrate was taken out of isopropanol, dried by nitrogen blow, and UV ozone washed for 20 minutes.
[4] The substrate after UV ozone cleaning was dust-removed by nitrogen blowing, and a 1% by mass magnesium acetate solution was spin-coated at 1300 rpm for 60 seconds. Then, annealing was performed on a hot plate at 150 ° C. for 1 hour.
[5] The annealed substrate was rinsed with ultrapure water and annealed on a hot plate at 150 ° C. for 30 minutes.
[6] Next, in order to form the layer 4 of the nitrogen-containing film, polyethyleneimine (registered trademark: Epomin) manufactured by Nippon Catalyst Co., Ltd. diluted to 0.1% by mass with ethanol was spin-coated at 2000 rpm for 30 seconds. did. The epomin used here was P1000 (branched structure) having a weight average molecular weight of 70,000.
[7] The thin film (substrate) produced in [6] was annealed on a hot plate in the atmosphere at 150 ° C. for 10 minutes.
[8] Next, the substrate subjected to the treatment of [7] is introduced into the vacuum apparatus, and the pressure is reduced to 5 × 10 ^-5 Pa or less. KHLHS-01 was laminated as an electron transport layer by a 15 nm vacuum deposition method, and then annealed at 125 ° C. for 20 minutes. After the substrate was introduced into the vacuum apparatus again and the pressure was reduced to 5 × ^10-5 Pa or less, α-NPD: KHLHS-04: KHLDR-03 was used as the light emitting layer, and α-NPD was used as the hole transport layer at 30 nm in order. , 24 nm vacuum deposition method.
[9] Next, a second metal oxide layer 6 was formed on the organic compound layer 5. Here, molybdenum oxide was formed by a vacuum vapor deposition method, which is a 10 nm vapor phase film forming method.
[10] Next, as a final step, the anode 7 was formed on the second metal oxide layer 6. Here, aluminum was formed into a film by a 100 nm vacuum deposition method.
The organic electroluminescent device 1 was produced by the above steps [1] to [10].
[11] According to the following <Measurement of light emission characteristics of organic electroluminescent element> and <Measurement of life characteristics of organic electroluminescent element>, the characteristics of the organic electroluminescent element 1 (voltage-luminance characteristic, under constant current density (equivalent to 1000 cd / m ^2)). ) Changes in brightness and voltage over time) were evaluated. The results are shown in FIG.
<Measurement of light emission characteristics of organic electroluminescent device>
A voltage was applied to the element and a current was measured by a "2400 type source meter" manufactured by Keithley. The emission brightness was measured by "BM-7" manufactured by Topcon. The measurement was performed in an argon atmosphere.
<Measurement of life characteristics of organic electroluminescent device>
A voltage was applied to the element and the relative brightness was measured by an "organic EL life measuring device" manufactured by System Giken. In this device, the relative brightness can be measured by a photodiode while automatically adjusting the voltage so that a constant current flows through the element. The current value was set for each element so that the brightness at the start of measurement was 1000 cd / m ² .

(Example 2)
The organic electroluminescent device 2 was produced in the same manner except that the step [7] of Example 1 was changed to the following [7-2], and the characteristics were evaluated. The results are shown in FIG.
[7-2] The thin film (substrate) produced in [6] was annealed on a hot plate under nitrogen at 150 ° C. for 10 minutes.

(Example 3)
An organic electroluminescent device 3 was produced in the same manner except that step [7] of Example 1 was omitted, and its characteristics were evaluated. The results are shown in FIG.

(Comparative Example 1)
The comparative organic electroluminescent device 1 was produced in the same manner except that the step [6] of the first embodiment was changed to the following [6-2] and the step [11] was changed to the following [11-2], and the characteristics were evaluated. Was done. The results are shown in FIG.
[6-2] Next, in order to form the layer 4 of the nitrogen-containing film, polyethyleneimine (registered trademark: Epomin) manufactured by Nippon Catalyst Co., Ltd. diluted to 0.4% by mass with ethanol was diluted at 2000 rpm for 30 seconds. Spin coated. The epomin used here was P1000 having a molecular weight of 70,000.
[11-2] The organic electroluminescent device characteristics (voltage-luminance characteristic) were measured by the following <Measurement of light emitting characteristics of the organic electroluminescent device>.
<Measurement of light emission characteristics of organic electroluminescent device>
A voltage was applied to the element and a current was measured by a "2400 type source meter" manufactured by Keithley. The emission brightness was measured by "BM-7" manufactured by Topcon. The measurement was performed in an argon atmosphere.

(Example 4)
The organic electroluminescent device 4 was produced in the same manner except that the step [6] of Example 1 was changed to the following [6-3], and the characteristics were evaluated. The results are shown in FIG.
[6-3] Next, in order to form the layer 4 of the nitrogen-containing film, polyethyleneimine (registered trademark: Epomin) manufactured by Nippon Catalyst Co., Ltd. diluted to 0.1% by mass with ethanol was diluted at 2000 rpm for 30 seconds. Spin coated. The epomin used here was P1000 having a molecular weight of 70,000. The substrate after spin coating was rinsed with ethanol.

(Example 5)
The organic electroluminescent device 5 was produced in the same manner except that the step [6] of Example 1 was changed to the following [6-4], and the characteristics were evaluated. The results are shown in FIG.
[6-4] Next, in order to form the layer 4 of the nitrogen-containing film, polyethyleneimine (registered trademark: Epomin) manufactured by Nippon Catalyst Co., Ltd. diluted to 0.1% by mass with ethanol was diluted at 2000 rpm for 30 seconds. Spin coated. The epomin used here was SP006 (branched structure) having a weight average molecular weight of 600. The substrate after spin coating was rinsed with ethanol.

(Example 6)
An organic electroluminescent device 6 was produced in the same manner except that the step [6] of Example 1 was changed to the following [6-5], and the characteristics were evaluated. The results are shown in FIG.
[6-5] Next, in order to form the layer 4 of the nitrogen-containing film, linear polyethyleneimine having a weight average molecular weight of 11000 diluted to 0.1% by mass with ethanol was spin-coated at 3000 rpm for 30 seconds. did. The substrate after spin coating was rinsed with ethanol.

(Example 7)
The organic electroluminescent device 7 is similarly changed except that the step [6] of the first embodiment is changed to the following [6-6], the step [11] is changed to the above [11-2], and the step [7] is omitted. Was prepared and its characteristics were evaluated. The results are shown in FIG.
[6-6] Next, the substrate was exposed to the vapor of diethylenetriamine for 0.5 hours in order to form the layer 4 of the nitrogen-containing film.

(Example 8)
The organic electroluminescent device 8 is similarly changed except that the step [6] of the first embodiment is changed to the following [6-7], the step [11] is changed to the above [11-2], and the step [7] is omitted. Was prepared and its characteristics were evaluated. The results are shown in FIG.
[6-7] Next, the substrate was exposed to the vapor of diethylenetriamine for 4 hours in order to form the layer 4 of the nitrogen-containing film.

(Comparative Example 2)
The comparative organic electroluminescent device 2 was produced in the same manner except that the steps [6] and [7] of the first embodiment were omitted and the step [11] was changed to the above [11-2], and the characteristics were evaluated. The results are shown in FIG.

(Comparative Example 3)
The comparative organic electric field is similarly changed except that the step [6] of the first embodiment is changed to the following [6-8], the step [7] is omitted, and the step [11] is changed to the above [11-2]. The light emitting element 3 was manufactured and its characteristics were evaluated. The results are shown in FIG.
[6-8] The substrate was then exposed to the vapor of diethylenetriamine for 24 hours to form layer 4 of the nitrogen-containing film.

(Example 9)
The organic electroluminescence is carried out in the same manner except that the step [6] of the first embodiment is changed to the following [6-9], the step [7] is omitted, and the step [11] is changed to the above [11-2]. The element 9 was manufactured and its characteristics were evaluated. The results are shown in FIG.
[6-9] Next, in order to form layer 4 of the nitrogen-containing film, pentamethyldiethylenetriamine diluted to 1.0% by mass with ethanol was spin-coated at 2000 rpm for 30 seconds.

(Example 10)
The organic electroluminescent device 10 was produced in the same manner except that the step [7] of Example 1 was changed to the following [7-3], and the characteristics were evaluated. The results are shown in FIG.
[7-3] The thin film (substrate) produced in [6] was annealed on a hot plate in the atmosphere at 150 ° C. for 2 hours.

(Example 11)
The organic electroluminescent device 11 was produced in the same manner except that the step [7] of Example 1 was changed to the following [7-4], and the characteristics were evaluated. The results are shown in FIG.
[7-4] The thin film (substrate) prepared in [6] was annealed on a hot plate under nitrogen at 150 ° C. for 2 hours.

The results of FIGS. 2 to 4 will be described below.
These are the characteristics evaluation results of devices with different annealing conditions after forming a nitrogen-containing film. FIG. 2 (element 1) is under the atmosphere, FIG. 3 (element 2) is under nitrogen, and FIG. 4 (element 3) is an annealing step. It is the result of the element without. Each of them starts emitting light from a low voltage and has achieved sufficient brightness. At the same time, it became clear that a reasonable life was achieved. Further, it is known that the film thicknesses of the respective nitrogen-containing films are 1.77, 2.13, and 2.28 nm, which are all thin films of less than 3 nm, and the thin films of less than 3 nm are high-performance organic electroluminescent devices. Can be seen that has been realized.
These differences in film thickness are considered to be due to the film thickness phenomenon due to annealing. It is presumed that the large decrease in film thickness in the atmosphere is due to the reaction with oxygen in the atmosphere. In addition, it is conceivable that the film thickness decrease due to annealing under nitrogen is caused by the removal of residual solvent and the rearrangement of polyethyleneimine due to heating. Therefore, it is considered that the film thickness was in the order of air, nitrogen, and no annealing in order from the thinnest. In addition, it is presumed that the slight variation in film thickness under the atmosphere is due to the reaction.
Although the elements 1 to 3 have certain characteristics or more, the characteristics are superior or inferior among them. For example, from the viewpoint of brightness under a certain voltage and element life under constant current drive, in the atmosphere and Annealing under nitrogen and no annealing are equivalent and have high characteristics.

Next, the results of FIGS. 5 and 6 will be described.
FIG. 5 shows the results of an element (comparative element 1) that does not correspond to the organic electroluminescent device of the present invention, in which only the film thickness was increased to 4.50 nm under the same optimum conditions for producing a nitrogen-containing film as in FIG. 3 (element 2). is there. It can be seen that the emission threshold voltage increases by about 0.5 V and the emission brightness at 6 V decreases by about 3000 cd / m ² .
On the contrary, FIG. 6 shows the result of examining the thinner part of the nitrogen-containing film under the optimum conditions. It can be seen that the film thickness is 1.76 nm, which is as thin as annealing in the atmosphere, while the characteristics such as brightness and life are higher than those of any of FIGS. 2 to 5.
From these results, it was shown that although an organic electroluminescent device having sufficiently high characteristics can be obtained at 3 nm or less, annealing in a thinner region and under nitrogen is particularly suitable.

Next, the results of FIGS. 7 and 8 will be described.
Polyethyleneimine having a branched structure having a weight average molecular weight of 600 and polyethyleneimine having a linear structure having a weight average molecular weight of 11000, respectively. It can be seen that all of them show good EL characteristics.

Next, the result of FIG. 9 will be described.
FIG. 9 shows the measurement results of the elements 7 and 8 in which the diethylenetriamine film was formed, the comparison element 3 and the comparison element 2 in which the nitrogen-containing film was not formed as the model substance obtained by cutting out the partial unit of polyethyleneimine. As a film-forming method, a method of exposing to steam was used here. Of course, the present invention is not limited to this, and a general film forming method such as spin coating used for producing a coating film can be used. When exposed to steam, the film thickness can be controlled by that time. The one exposed to steam for 0.5 hours (element 7) was 1.60 nm, the one exposed to steam for 4 hours (element 8) was 1.82 nm, and the one exposed to steam for 24 hours (comparative element). 3) was 7.17 nm. By the way, the untreated one (comparative element 2) was observed to be 0.04 nm, indicating that it can be measured with high accuracy. The 1 nm range, which was good even with the spin coating of polyethyleneimine, showed good characteristics with this material. The emission threshold voltage was better for 0.5 hours of exposure, but the brightness at 6 V was better for 4 hours of exposure. It is speculated that this difference comes from the difference in membrane structure. On the other hand, the device exposed for 24 hours is inferior in both the emission threshold voltage and the brightness under 6 V as compared with the device without treatment. Again, it was shown that the film thickness of 3 nm or less was good.

Next, the result of FIG. 10 will be described.
FIG. 10 shows the characteristic evaluation results of the device 9 produced by spin-coating by changing the model material forming the nitrogen-containing film to pentamethyldiethylenetriamine composed of only tertiary amines. Although the film thickness is extremely thin at 0.16 nm, it has been proved that the characteristics can be improved as compared with the element without treatment (comparative element 2). From this, it was clarified that the characteristics can be expected to be improved even in an extremely thin region of less than 1 nm.

Finally, the results of FIGS. 11 and 12 will be described.
In FIG. 11, three elements 2 and three elements 3 of Examples 2 and 3 are manufactured, the brightness under 5 V is measured, and the variation in characteristics is compared. It can be seen that the results of annealing under nitrogen are similar to the results without annealing. This is considered to suggest that annealing has the effect of reducing variation. That is, it can be seen that the process stability is improved by annealing. This is presumed to be the effect of rearrangement due to annealing.
FIG. 12 shows the results of examining the environment dependence of annealing with high process stability. In each of the environments under the atmosphere and nitrogen, the number of the element 1 which was annealed for 10 minutes, the element 2 and the element 10 and the element 11 which were annealed for 2 hours were produced as shown in the margin of FIG. 12, and under 5 V. It is a comparison of the brightness in. It can be seen that long-term annealing is not good in any environment. However, annealing in the atmosphere has deteriorated more, and has deteriorated to the extent that it hardly emits light. In that respect, annealing under nitrogen still produces sufficient brightness, although the brightness is reduced.
From FIGS. 11 and 12, it can be said that annealing under nitrogen is excellent in process stability.

From the above, it was shown that the low molecular weight to high molecular weight material having a polyethyleneimine skeleton exhibits good properties in a thin film region of 0.1 nm to less than 3 nm.
In addition, among them, the thinner film is better, and the film-forming process can obtain good characteristics not only by a general coating process but also by other methods such as exposure to steam, which is a vapor-phase film-forming process. Became clear. As a subsequent process, it was found that annealing under nitrogen is also good in process stability.

1: Substrate 2: Cathode 3: First metal oxide layer 4: Nitrogen-containing film layer 5: Organic compound layer 6: Second metal oxide layer 7: Anode

Claims (5)

An organic electroluminescent device having a structure in which a plurality of layers are laminated between an anode and a cathode formed on a substrate.
The organic electroluminescent device has a metal oxide layer between the anode and the cathode.
An organic electroluminescent device characterized by having a nitrogen-containing film having an average thickness of 0.1 nm or more and less than 3 nm on the anode side adjacent to the metal oxide layer. The organic electroluminescent device according to claim 1, wherein the nitrogen-containing film is a film derived from a nitrogen-containing compound having a primary amine structure. The organic electroluminescent device according to claim 1 or 2, wherein the nitrogen-containing compound is polyethyleneimine or diethylenetriamine. The organic electroluminescent device according to claim 1 or 2, wherein the nitrogen-containing compound is polyethyleneimine having a branched structure and a weight average molecular weight thereof is 100 to 1000. The organic electroluminescent device according to any one of claims 1 to 4, wherein the nitrogen-containing film is formed by decomposing a nitrogen-containing compound by heating.

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